DNS
DNS means Domain Name System. It is the internet system that turns names such as example.com into technical records, including the IP addresses and mail routing information needed by browsers, email servers, and other software.
DNS Basics
Core DNS concepts, hierarchy entry points, resolvers, caching, and domain structure.
Root Servers
Root servers sit at the top of the public DNS hierarchy. They do not normally know the records for individual domains, but they know which TLD nameservers are responsible for zones such as com, uk, and org.
TLD
TLD means top-level domain, such as com, uk, or org. Root servers delegate TLDs, and TLD nameservers then delegate individual registered domains.
Registry
A registry operates a TLD, such as .com or .uk. The registry maintains the authoritative data for that TLD, including which nameservers are delegated for registered domains.
Registrar
A registrar is the company where a domain is registered and managed. Registrars submit delegation details to the registry, such as which nameservers should be used for the domain.
Apex / Zone Apex
The apex, or zone apex, is the bare domain itself, such as example.com. It is different from subdomains such as www.example.com or mail.example.com.
Subdomain
A subdomain is a name below another domain, such as mail.example.com under example.com. Subdomains can have their own records and, in some cases, their own delegated DNS zones.
TTL
TTL means time to live. It tells DNS resolvers how long they may cache a record before checking again. Lower TTLs update faster, while higher TTLs reduce query load.
Propagation
Propagation is the informal name people use for DNS changes becoming visible across the internet. In practice, most delays are caused by resolver caches holding old answers until their TTL expires.
Recursive Resolver
A recursive resolver performs DNS lookups on behalf of users and applications. It follows the chain from root servers to TLD servers to authoritative nameservers, then usually caches the answer for future queries.
Public Resolver
A public resolver is a recursive resolver offered for general use, such as Cloudflare 1.1.1.1 or Google 8.8.8.8. Public resolvers can be useful for comparison when troubleshooting DNS answers.
Local Resolver
A local resolver is the DNS resolver supplied by a router, ISP, office network, VPN, or device configuration. It may apply local filtering, caching, split DNS, or other network-specific behaviour.
Authoritative Answer
An authoritative answer comes from a nameserver responsible for the zone being queried. It is different from a cached answer returned by a recursive resolver.